There are a number of situations in which it is desirable to electrically stimulate tissue of a living body. Target tissues for stimulation can include skeletal muscle, smooth muscle, nerves and organs. In addition, organs such as the stomach and heart can respond to therapy that includes electrical stimulation. It is often desirable to implant stimulating electrodes in or proximate to the target tissue. It is also often desirable to stimulate the target tissue without stimulating neighboring tissues.
An application in which it is desirable to stimulate a region of target tissue while avoiding stimulation of surrounding tissue is stimulation of the myocardium. For example, following a heart attack, cardiac tissue can become necrotic and cease contributing to hemodynamic function. Numerous morbid conditions are sequelae of the loss of hemodynamic function. The necrosis can be treated with cell therapy, which involves transplanting cells into the damaged myocardium to repopulate the damaged region. In one procedure, cells are transplanted by injection directly into or proximate to the affected tissue. Electrical stimulation of the region having the transplanted cells can cause the transplanted cells to contract and assist in hemodynamic function. Electrical stimulation might also increase the cell viability, cell engraftment and cell proliferation. The cells transplanted include but are not limited to skeletal myoblast cells, cardiac myoblast cells and stem cells.
In such a case, it is desirable to electrically stimulate the region with the transplanted cells, but not the heart as a whole. Stimulation of the heart as a whole can cause unwanted or poorly timed contractions of the heart, and possibly life-threatening conditions such as ventricular fibrillation.
Similar concerns can apply in other applications as well. It may be desirable to implant electrodes in the wall of the stomach, for example, to induce contraction or other physiological effect, without stimulating neighboring muscles, organs or nerves.